The use of fans to move air through heat exchangers is well known, for example in the field of air conditioning and the field of motor vehicle cooling. A fan for such an application may consist of a hub member and plural blade members, each blade member having a root portion and a tip portion, the root portions of each blade being secured to the hub portion such that the blades extend substantially radially of the hub portion. A blade tip support ring may link the blades near to, or more usually, at their tip portions.
Such a fan, which is often driven by an electric motor, or via a transmission from an associated engine, is usually disposed so that the fan radial plane extends parallel to a face portion of the associated heat exchanger.
Fans of this type are commonly referred to as "axial flow fans". However, although the blades are pitched so as to move air in an axial direction, nevertheless the action of the fan causes a relatively complicated air flow. It will, for example, be apparent that rotation of the fan causes air which has passed through the fan to have a rotational component of motion, due to the movement of the blades, as well as a linear component induced by the pitch of the blades. Leakage of air around the fan blade tips (so-called tip vortices) between the high and low pressure sides of the fan may also occur.
Furthermore, the particular blade form and the particular blade disposition selected for a fan, for example the dihedral angle of the blade, the variation in pitch along the blade span or the chord length of the blade (taken along a radial cross section) will affect the pressure distribution provided immediately adjacent the fan, and hence will affect the flow of air which has passed through the fan.
A fan of the type used to move air through a heat exchanger is intended to provide air flow in an axial direction; components in other directions are wasteful of energy. Such wasteful components of air flow impinge upon the various mechanical structures around the heat exchanger and upon the heat exchanger itself to increase the overall noise produced by the system.
It is accordingly an object of the present invention to at least partially mitigate the above mentioned difficulties.